Automotive fuel, primarily gasoline, is a volatile liquid subject to potentially rapid evaporation, in response to diurnal variations in the ambient temperature. Thus, the fuel contained in automobile gas tanks presents a major source of potential evaporative emission of hydrocarbons into the atmosphere. Such emissions from a vehicle constitute what is technically called as ‘evaporative emissions’. Even if the vehicle's engine is turned off, these fuel vapors are produced.
Industry's response to this potential problem has been the incorporation of the evaporative emission control systems (EVAP) into automobiles, to prevent fuel vapor from being discharged into the atmosphere. The EVAP systems include a canister containing adsorbent carbon (i.e., carbon canister) that traps those fuel vapors and feeds them back to the intake manifold of the engine of the vehicle for combustion, thus, reducing evaporative emissions from the vehicle.
Hybrid electric vehicles, including plug-in hybrid electric vehicles (HEV's or PHEV's), pose a particular problem for effectively controlling evaporative emissions with this kind of system. Although hybrid vehicles have been proposed and introduced having a number of forms, these designs share the characteristic of providing a combustion engine as backup to an electric motor. Primary power is provided by the electric motor, and careful attention to charging cycles can result in an operating profile in which the engine is only run for short periods. Systems in which the engine is only operated once or twice every few weeks are not uncommon. Purging the carbon canister can only occur when the engine is running, of course, and if the canister is not purged, the carbon pellets can become saturated, after which hydrocarbons will escape to the atmosphere, causing pollution.
Further, PHEVs have a sealed fuel tank designed to withstand differences in pressure and vacuum within the tank resulting from diurnal ambient temperature variations. A Fuel tank pressure transducer (FTPT), being a high pressure sensor, is generally disposed within the tank, to measure the pressure within the interior of the tank. Performing a rationality test to ensure effective operation of the FTPT is difficult in PHEVs, as the tank cannot be easily vented. In any event, venting would not be desirable, as that action could cause hydrocarbons to be eventually emitted to the atmosphere, causing pollution.
Considering the problems mentioned above, and other shortcomings in the art, there exists a need for a more effective and efficient system and method for ensuring reliable operations of the fuel tank pressure transducer positioned within the fuel tank of a vehicle.